Chapter 16 Vocabulary Absolute & Relative Dating

cross cutting relationships (Hutton)

an igneous intrusion (dike) or a fault must be younger than the rocks they cut across

uniformitarianism

basic principle of geology stating that earth processes occurring today are similar to those that occurred in the past

mold

cavity in rock that has the shape of a fossil that was trapped there; water dissolved the fossil away, leaving its imprint

extinct

describes an organism species that no longer lives anywhere on earth

absolute dating

determining the ages of rocks using the radioactive decay in them

relative dating

determining the order of events and the relative age of rocks (older or younger) by examining the positions of rocks in layers

carbonaceous film

fossil impression in rock, consisting only of a thin carbon deposit

index fossil

fossil of a species that existed briefly and was widespread geographically, used in determining the relative ages of rock layers

Law of Superposition

law stating that, in layers of undisturbed rock, the oldest are on the bottom, and rocks become younger toward the top

unconformity

one or more missing layers in a sequence of rocks; this is a result of a gap in the time record

petrified remains

plant or animal remains that have been petrified, or "turned to rock"; this happens when minerals carried in groundwater replace the original material

fossil

remains or traces of a once-living organism; usually preserved in rock

radioactive decay

the decay of an atom of one element to form another element, occurring when an alpha particle or beta particle is expelled from the original atom

half life

the time it takes for half of the atoms of an isotope in an object to decay

cast

type of fossil formed when an earlier fossil in rock is dissolved away, leaving behind the impression of that fossil (a mold), and new sediments or minerals enter the mold